Image sensor arrays typically comprise a linear array of photosensors which raster scan an image-bearing document and convert the microscopic image areas viewed by each photosensor to image signal charges. Following an integration period, the image signal charges are amplified and transferred as an analog video signal to a common output line or bus through successively actuated multiplexing transistors.
For high-performance image sensor arrays, a preferred design includes an array of photosensors of a width comparable to the width of a page being scanned, to permit one-to-one imaging generally without the use of reductive optics. In order to provide such a “full-width” array, however, relatively large silicon structures must be used to define the large number of photosensors. A preferred technique to create such a large array is to make the array out of several butted silicon chips. In one proposed design, an array comprises of 20 silicon chips, butted end-to-end, each chip having 372 active photosensors spaced at 600 photosensors per inch.
Besides photosensor arrays, there are other types of multi-chip systems useful in recording or making images. In xerographic systems, there can be provided “LED arrays,” meaning chips in which a linear array of a laser emitters are used to discharge imagewise areas on a photoreceptor for xerographic printing purposes. Also, many designs of ink-jet printheads include, on a chip, a series of independently-addressable ink-jet emitters.
Whether an imaging chip is used for recording images or creating images, a common feature in such chips is the use of a shift register, the stages of the shift register being in various possible ways associated with the different “imaging elements” (e.g., photosensors, light emitters, ink-jet emitters, and associated circuitry), so that individual imaging elements can be addressed at various times, such as for image input or image readout.
Imaging systems of various types typically require a “clock signal” of predetermined frequency to enable orderly transfer (in or out) of image data, such as with a shift register. A typical clock signal used in digital systems is a 5-volt square wave of predetermined frequency. One practical difficulty of using a digital square wave comes from the fact that abrupt changes in voltages cause transients to be associated with the power supply for the whole system; these transients in turn can be associated with noticeable signatures at the rising edge and trailing edge of each pulse.
U.S. Pat. No. 6,958,833 shows an imaging chip, in this case a photosensor array chip, where a plurality of local clock drivers, each clock driver operative of a small subset of photosensors, are selectable, so that only photosensors needed for a particular imaging purpose, such as scanning a small document, are used to generate image signals.